{"id":712,"date":"2013-11-29T15:21:05","date_gmt":"2013-11-29T23:21:05","guid":{"rendered":"http:\/\/galencharlton.com\/blog\/?p=712"},"modified":"2013-11-29T15:21:05","modified_gmt":"2013-11-29T23:21:05","slug":"notes-from-code4lib-bc-gluing-together-an-ugly-string-to-emit-rdf","status":"publish","type":"post","link":"https:\/\/galencharlton.com\/blog\/2013\/11\/notes-from-code4lib-bc-gluing-together-an-ugly-string-to-emit-rdf\/","title":{"rendered":"Notes from Code4Lib BC: gluing together an ugly string to emit RDF"},"content":{"rendered":"

This afternoon I’m sitting in the new bibliographic environment breakout session at Code4Lib BC. After taking a look at Mark Jordan’s easyLOD<\/a>, I decided to play around with putting together a web service for Koha that emits RDF when fed a bib ID. Unlike Magnus Enger’s semantikoha<\/a> prototype, which uses a Ruby library to convert MARC to RDF, I was trying for an approach that used only Perl (plus XS).<\/p>\n

There were are of building blocks available. Putting them together turned out to be a tick more convoluted than I expected.<\/p>\n

The Library of Congress has published an XSL stylesheet<\/a> for converting MODS to RDF. Converting MARC(XML) to MODS is readily done using other stylesheets<\/a>, also published by LC.<\/p>\n

The path seemed clear for a quick-and-dirty prototype — make a copy of svc\/bib<\/code>, copy it to opac\/svc\/bib<\/code> and take out the bits for doing updates (we’re not quite ready to make cataloging that<\/strong> collaborative!), and write a few lines to apply two XSLT transformations.<\/p>\n

The code was quickly written — but it didn’t work. XML::LibXSLT<\/code>, which Koha uses to handle XSLT, complained about the modsrdf.xsl<\/code> stylesheet. Too new! That stylesheet is written in XSLT 2.0, but libxslt<\/code>, the C library that XML::LibXSLT<\/code> is based on, only supports XSLT 1.<\/p>\n

As it turns out, Perl modules that can handle XSLT are rather thin on the ground. What I ended up doing was:<\/p>\n

Installing XML::Saxon::XSLT2<\/a>, which required…<\/p>\n

Installing Saxon-HE<\/a>, a Java XML and XSLT processor that supports XSLT 2.0, which required…<\/p>\n

Installing Inline::Java<\/a>, which required…<\/p>\n

Installing a JDK (I happened to choose OpenJDK<\/a>).<\/p>\n

After all that (and a quick tweak to the modsrdf.xsl<\/code> stylesheet, I ended up with the following code that did the trick:<\/p>\n

\r\n#!\/usr\/bin\/perl\r\n\r\nBEGIN {\r\n    $ENV{'PERL_INLINE_DIRECTORY'} = '\/tmp\/inline';\r\n}\r\n\r\nuse Modern::Perl;\r\n\r\nuse CGI;\r\nuse C4::Biblio;\r\nuse C4::Templates;\r\nuse XML::Saxon::XSLT2;\r\n\r\nmy $query = new CGI;\r\nbinmode STDOUT, ':encoding(UTF-8)';\r\n\r\n# do initial validation\r\nmy $path_info = $query->path_info();\r\n\r\nmy $biblionumber = undef;\r\nif ($path_info =~ m!^\/(\\d+)$!) {\r\n    $biblionumber = $1;\r\n} else {\r\n    print $query->header(-type => 'text\/xml', -status => '400 Bad Request');\r\n}\r\n\r\n# are we retrieving or updating a bib?\r\nif ($query->request_method eq \"GET\") {\r\n    fetch_rdf($query, $biblionumber);\r\n}\r\n\r\nexit 0;\r\n\r\nsub fetch_rdf {\r\n    my $query = shift;\r\n    my $biblionumber = shift;\r\n    my $record = GetMarcBiblio($biblionumber);\r\n    if  (defined $record) {\r\n        print $query->header(-type => 'text\/xml');\r\n        my $xml = $record->as_xml_record();\r\n        my $base = join('\/',\r\n                        C4::Context->config('opachtdocs'),\r\n                        C4::Context->preference('opacthemes'),\r\n                        C4::Templates::_current_language()\r\n                       );\r\n        $xml = transform($xml, \"$base\/xslt\/MARC21slim2MODS3-3.xsl\");\r\n        $xml = transform($xml, \"$base\/xslt\/modsrdf.xsl\");\r\n        print $xml;\r\n    } else {\r\n        print $query->header(-type => 'text\/xml', -status => '404 Not Found');\r\n    }\r\n}\r\n\r\nsub transform {\r\n    my $xmlrecord = shift;\r\n    my $xslfilename = shift;\r\n\r\n    open my $fh, '<', $xslfilename;\r\n    my $trans = XML::Saxon::XSLT2->new($fh);\r\n    return $trans->transform($xmlrecord);\r\n\r\n}\r\n<\/pre>\n
This works… but is not satisfying.  Making Koha require a JDK just for XSLT 2.0 support is a bit much, for one thing, and it would likely be rather slow if used in production.  It’s a pity that there’s still no broad support for XSLT 2.0.<\/p>\n
A dead end, most likely, but instructive nonetheless.<\/p>\n
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